The invention involves a press device for multi-sided coating of workpieces, especially table board-shaped pieces of furniture, on their upper side and side surfaces, whereby the workpieces lie next to each other on a supporting system that has many supporting bolts distributed in a grid-like manner, which can be adjusted between a passive position out of contact with the workpieces and a coating position that supports the workpieces.
The main application of the invention is the coating of three-dimensional pieces of furniture that should not only be coated on their front, but also on the surrounding side surfaces, with a plastic film, a veneer, or the like. In the following, the discussion involves only a film, without intending to be restrictive to the invention. The coating is done by the application of heat and pressure in a press. So that its capacity can be used optimally, for the most part, numerous workpieces are fed together on a shared pallet to the supporting system of the press, and are coated there together. After leaving the press, the workpieces are then separated by cutting them out from the attached film.
So that the plastic film can be properly placed not only on the upper side of the workpieces, but also on the side surfaces that are set back from it, especially on its lower edge, the workpieces must be separated at a distance from their substrate. This is done for the most part by supporting bolts in the form of lifting bolts, which travel into an upper position and in this way lift up the workpieces. It is essential in the process that the lifting bolts that are lifted into the upper coating position are only those which are covered completely by a workpiece, while the lifting bolts that are not covered or not completely covered stay in the lower resting position, so that the coating process is not impaired on the side edge surfaces.
Independently from that, it is also disruptive if free-standing, uncovered supporting bolts are in their upper position during the coating operation, because these bolts are also coated by the film at the same time and the film must then be separated again with difficulty and in a time-consuming manner.
In the state of the art, numerous press devices have already been described, which take into account the aforementioned set of problems. As examples, reference is made to the patents DE-A-197 18 561 and 198 36 219 of the same applicant.
In the majority of cases, these press devices operate absolutely flawlessly. However, there are still quality problems that result individually in the coating of the corner areas. Tests by the applicant have revealed that under unfavorable circumstances, an over-stretching and tearing of the film can occur locally here.
The object of the invention presented here is therefore to create a remedy for this, i.e. to ensure a reliable and lasting coating especially on the side edges and corners even in the case of unfavorable conditions.
This object is achieved according to the invention in that above the supporting bolts, an elastic membrane is arranged on which the workpieces can be supported.
The invention is based on the discovery that the set of problems described is not only influenced by the extent of the stretching, but also by the speed at which the film is stretched. This stretching speed is now reduced according to the invention by the intermediately placed elastic membrane, since in the edge area of the workpieces, where the film is pulled into the intermediate space not only between adjacent workpieces, but also between adjacent supporting bolts, the membrane functions as a support. It can be said that the membrane acts in these areas as a stretching brake and a guide for the film.
Another important aspect of the invention is provided in that the membrane prevents a direct contact of the heated film with the cold substrate of the workpieces, in particular the pallet; and the film can thus not be chilled in the greatly stretched areas and keeps its elastic properties to a greater extent than in the prior art.
So that the membrane must not be re-aligned for each coating operation, it is recommended that it is attached to the press device or a removable pallet with a grid-like perforated board. In this manner, a slight pre-tension is sufficient so that a fold formation in the membrane is prevented.
It is especially preferred to attach the membrane on its edge to the surrounding frame of the pallet in such a way that it runs at a certain distance above the perforated board of the pallet, and especially at the approximate height occupied by the upper ends of the lifting dies, when the lifting dies are in the coating position. Instead of this, the membrane can however also be supported on the perforated board and be attached to the edge of the perforated board by clamping rails or the like, in particular, if work is done with horizontally adjustable supporting dies.
An expedient further embodiment of the invention provides that the membrane is made of a transparent material. In this way, it can be recognized through the membrane from above where the positions of the supporting bolts are and the workpieces can be positioned accordingly. Moreover, the transparence of the membrane has the advantage that for supporting systems with bolts that can be moved horizontally, it can be recognized from above which bolts are projecting on the edge of the workpieces and accordingly must be pushed out of the way. Pushing them out of the way can be done in spite of the membrane, since it consists of a sufficiently flexible material, for example, out of silicone, rubber, or the like.
Since the membrane is exposed to a certain amount of wear, it is recommended to attach it so that it can be replaced. If the membrane is mounted onto a pallet, then it can be made in multiple parts, so that a replacement is possible without a great expense.
Normally, the pallet is a separate part, which is covered outside of the pressing operation with the workpieces to be coated and then placed into the press device. The use of the membrane according to the invention is, however, also possible, of course, if the pallet is a fixed component of the press device.
It is customary to promote the coating operation in such a manner that the space under the film is connected at partial vacuum, so that the film is supported better on the workpiece edges. So that this principle can also be applied for pallets with an integrated membrane, it is recommended to perform the partial vacuum connection of the pallet in such a way that the partial vacuum impingement takes place in the space below the membrane and that the membrane has openings. In this way, the film itself is sucked onto the workpiece edges and the membrane can not speed on ahead.